Size of Bicelle Defects Probed via Diffusion Nuclear Magnetic Resonance of PEG

Soong, Ronald; Majonis, Daniel; Macdonald, Peter M.

doi:10.1016/j.bpj.2009.05.034

Cited by 9 publications

(9 citation statements)

References 82 publications

(106 reference statements)

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“…The simulations confirm the conclusions of Triba et al that DHPC is quite likely to mix with DMPC in the bilayer region to a nonnegligible degree. Although the decrease in pore size with decreasing DHPC fraction appears to be in line with recent experimental findings (19), this agreement may only be a trivial result of the artificially fixed ratio of one pore per 128 lipids imposed by the simulation's periodic boundary conditions.…”

Section: Thermodynamic Stability Of the Edgesupporting

confidence: 87%

“…Early descriptions of aggregate structure and the distribution of lipids within the aggregates were based on a very simple ideal bicelle model, in which total segregation of DHPC and DMPC between edge and bilayer environments was assumed (14). Recent work has highlighted the morphological complexity of these systems, with disks, wormlike or ribbonlike micelles, and perforated bilayer or networklike structures appearing at various compositions and temperatures (15)(16)(17)(18)(19)(20). The extent of mixing of long-and short-tail PC lipids within these structures-the degree of deviation from the ideal bicelle model-has also been inferred and quantified using phosphorus NMR (21,22).…”

Section: Introductionmentioning

confidence: 99%

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Atomistic Simulations of Bicelle Mixtures

Jiang

Wang

Kindt

2010

Biophysical Journal

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Mixtures of long- and short-tail phosphatidylcholine lipids are known to self-assemble into a variety of aggregates combining flat bilayerlike and curved micellelike features, commonly called bicelles. Atomistic simulations of bilayer ribbons and perforated bilayers containing dimyristoylphosphatidylcholine (DMPC, di-C(14) tails) and dihexanoylphosphatidylcholine (DHPC, di-C(6) tails) have been carried out to investigate the partitioning of these components between flat and curved microenvironments and the stabilization of the bilayer edge by DHPC. To approach equilibrium partitioning of lipids on an achievable simulation timescale, configuration-bias Monte Carlo mutation moves were used to allow individual lipids to change tail length within a semigrand-canonical ensemble. Since acceptance probabilities for direct transitions between DMPC and DHPC were negligible, a third component with intermediate tail length (didecanoylphosphatidylcholine, di-C(10) tails) was included at a low concentration to serve as an intermediate for transitions between DMPC and DHPC. Strong enrichment of DHPC is seen at ribbon and pore edges, with an excess linear density of approximately 3 nm(-1). The simulation model yields estimates for the onset of edge stability with increasing bilayer DHPC content between 5% and 15% DHPC at 300 K and between 7% and 17% DHPC at 323 K, higher than experimental estimates. Local structure and composition at points of close contact between pores suggest a possible mechanism for effective attractions between pores, providing a rationalization for the tendency of bicelle mixtures to aggregate into perforated vesicles and perforated sheets.

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Section: Thermodynamic Stability Of the Edgesupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Atomistic Simulations of Bicelle Mixtures

Jiang

Wang

Kindt

2010

Biophysical Journal

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“…4,13–19 At higher lipid-to-detergent q values (lipid-to-detergent mole ratio) bicelles are Swiss cheese-like perforated bilayer sheets in which the holes are edge-stabilized by detergent. 6,20–26 …”

Section: Introductionmentioning

confidence: 99%

“…Depending on composition and temperature, bicelles either tumble rapidly and isotropically in solution or form phases with high viscosity and long range order. 4,6,13–26 Indeed in the viscous q > 2 regime, bicelles can be uniformly aligned using high magnetic field. 1,5,27–28 Unlike lipoprotein-phospholipid nanodiscs that have a diameter fixed by the length of the apolipoprotein used to provide bilayer edge-stabilization, 29 the size of bicelles can be systematically varied by altering the lipid-to-detergent molar ratio.…”

Section: Introductionmentioning

confidence: 99%

Bicelles at Low Concentrations

Horn

Chen

et al. 2012

Mol. Pharmaceutics

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Bilayered detergent-lipid assemblies known as bicelles have been widely used as model membranes in structural biological studies and are being explored for wider applications, including pharmaceutical use. Most studies to date have involved the use of concentrated bicelle mixtures, such that little is known about the capacity of bicellar mixtures to be diluted without unwanted transitions to non-isotropic phases. Here, different detergent/lipid mixtures have been explored, leading to the identification of two different families of bicelles for which it is possible to lower the total amphiphile (detergent+lipid) concentration to <1% (w/v) while retaining isotropic assemblies. These include a novel family of bicelles based on mixtures of 6-cyclohexyl-1-hexylphosphocholine (Cyclofos-6) and the lipid dimyristoylphosphatidylcholine (DMPC). Bicelles formed by these mixtures can be diluted to <0.5% and also have attractive biochemical properties. However, a caveat of our results is that the diffusion coefficients measured for the lipid component of the different bicelles tested were seen to be dependent on sample history, even though all samples were optically transparent. This suggests that the phase behavior of bicelles at low lipid-to-detergent ratios may be more complex than previously appreciated.

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“…Bicellar mixtures comprising DMPC or DMPC- d 54 , DMPG, and DHPC have been studied using a variety of methods including SANS[51], [56], [58]–[61], pulsed field gradient NMR [62], [63], and 2 H or 31 P NMR [55], [57], [64]–[66]. The properties of such mixtures are well known and the transitions occur in an accessible temperature range.…”

Section: Introductionmentioning

confidence: 99%

Interaction of the C-Terminal Peptide of Pulmonary Surfactant Protein B (SP-B) with a Bicellar Lipid Mixture Containing Anionic Lipid

et al. 2013

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The hydrophobic lung surfactant SP-B is essential for respiration. SP-B promotes spreading and adsorption of surfactant at the alveolar air-water interface and may facilitate connections between the surface layer and underlying lamellar reservoirs of surfactant material. SP-B63–78 is a cationic and amphipathic helical peptide containing the C-terminal helix of SP-B. 2H NMR has been used to examine the effect of SP-B63–78 on the phase behavior and dynamics of bicellar lipid dispersions containing the longer chain phospholipids DMPC-d 54 and DMPG and the shorter chain lipid DHPC mixed with a 3∶1∶1 molar ratio. Below the gel-to-liquid crystal phase transition temperature of the longer chain components, bicellar mixtures form small, rapidly reorienting disk-like particles with shorter chain lipid components predominantly found around the highly curved particle edges. With increasing temperature, the particles coalesce into larger magnetically-oriented structures and then into more extended lamellar phases. The susceptibility of bicellar particles to coalescence and large scale reorganization makes them an interesting platform in which to study peptide-induced interactions between lipid assemblies. SP-B63–78 is found to lower the temperature at which the orientable phase transforms to the more extended lamellar phase. The peptide also changes the spectrum of motions contributing to quadrupole echo decay in the lamellar phase. The way in which the peptide alters interactions between bilayered micelle structures may provide some insight into some aspects of the role of full-length SP-B in maintaining a functional surfactant layer in lungs.

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Size of Bicelle Defects Probed via Diffusion Nuclear Magnetic Resonance of PEG

Cited by 9 publications

References 82 publications

Atomistic Simulations of Bicelle Mixtures

Atomistic Simulations of Bicelle Mixtures

Bicelles at Low Concentrations

Interaction of the C-Terminal Peptide of Pulmonary Surfactant Protein B (SP-B) with a Bicellar Lipid Mixture Containing Anionic Lipid

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